CODEWITHSUNDEEP
pythonregexstringlist
Hypothetical Ninja
Hypothetical Ninja

Reputation: 4077

Matching an expression using ReGex ,Python

I have many sentences , though i'd create a function that would operate on each sentence individually. so the input is just a string. My main objective is to extract the words that follow prepositions like in "near blue meadows" i'd want blue meadows to be extracted.
I have all my prepositions in a text file. it works fine but i guess there's a problem in the regex used . here's my code: import re

with open("Input.txt") as f:
    words = "|".join(line.rstrip() for line in f)
    pattern = re.compile('({})\s(\d+\w+|\w+)\s\w+'.format(words))
    text3 = "003 canopy grace appt, classic royale garden, hennur main road, bangalore 43. near hennur police station"
    print(pattern.search(text3).group())

This returns :

AttributeError                            Traceback (most recent call last)
<ipython-input-83-be0cdffb436b> in <module>()
      5     pattern = re.compile('({})\s(\d+\w+|\w+)\s\w+'.format(words))
      6     text3 = ""
----> 7     print(pattern.search(text3).group())

AttributeError: 'NoneType' object has no attribute 'group

The main problem is with regex , my expected output is "hennur police" i.e 2 words after near . In my code I have used ({}) to match from the list of preps, \s followed by space , (\d+\w+|\w+) followed by words like 19th or hennur , \s\w+ followed by a space and a word. My regex fails to match , hence the None error. Why is it not working?

The content of the Input.txt file:

['near','nr','opp','opposite','behind','towards','above','off']

Expected output:

hennur police

Upvotes: 1

Views: 193

Answers (1)

falsetru
falsetru

Reputation: 368954

The file contains Python list literal. Use ast.literal to parse the literal.

>>> import ast
>>> ast.literal_eval("['near','nr','opp','opposite','behind','towards','above','off']")
['near', 'nr', 'opp', 'opposite', 'behind', 'towards', 'above', 'off']

import ast
import re

with open("Input.txt") as f:
    words = '|'.join(ast.literal_eval(f.read()))
    pattern = re.compile('(?:{})\s(\d*\w+\s\w+)'.format(words))
    text3 = "003 canopy grace appt, classic royale garden, hennur main road, bangalore 43. near hennur police station"

    # If there could be multiple matches, use `findall` or `finditer`
    #   `findall` returns a list of list if there's capturing group instead of
    #   entire matched string.
    for place in pattern.findall(text3):
        print(place)

    # If you want to get only the first match, use `search`.
    #   You need to use `group(1)` to get only group 1.
    print pattern.search(text3).group(1)

output (The first line is printed in for loop, the second one come from search(..).group(1)):

hennur police
hennur police

NOTE you need to re.escape each word if there's any special character in the word that has special meaning in regular expression.

Upvotes: 1

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